Metal forming apparatus for producing metal ribbon fibers

ABSTRACT

The invention disclosed herein provides a metal forming apparatus with an improved chill block for continuous manufacturing of a multiplicity of metal ribbon fibers by providing a rotating chill block with alternate bands of high and low thermal capacity to allow shear between fibers in the high and the low conductivity bands.

'United States Patent [191 Mobley et al.

[ Oct. 28, 1975 METAL FORMING APPARATUS FOR PRODUCING METAL RIBBON FIBERS [75] Inventors: Carroll E. Mobley, Columbus;

Robert E. Maringer, Worthington, both of Ohio [73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

22 Filed: May 1, 1974 211 Appl. No.: 465,795

[52] US. Cl. 164/276; l64/87; 164/138 [51] Int. Cl. B22D 11/06; 322C l/lO [58] Field of Search 164/87, 138, 276

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,040,498 8/1966 United Kingdom 164/87 Primary ExaminerFrancis S. l-lusar Assistant ExaminerGus T. l-lampilos Attorney, Agent, or FirmR. S. Sciascia; R. E. ONeill [57] ABSTRACT The invention disclosed herein provides a metal forming apparatus with an improved chill block for continuous manufacturing of a multiplicity of metal ribbon fibers by providing a rotating chill block with alternate bands of high and low thermal capacity to allow shear between fibers in the high and the low conductivity bands.

6 Claims, 2 Drawing Figures METAL FORMING APPARATUS FOR PRODUCING METAL RIBBON FIBERS The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The deployment of chaff as passive reflectors of electromagnetic radiation is one of the major countermeasures presently employed by US. military forces to reduce the threat associated with enemy radar devices. Basically, chaff consists of discrete length strips of aluminum foil (i.e., ribbon fiber) or metallized glass fiber. The fibers are packaged in canisters which are machine dispersed from aircraft. After deployment, the canisters open to disperse the individual fibers and create a chaff cloud. While fibers of several preselected lengths (i.e., a mix) are packaged in the chaff containers, the capability for on-site selection and deployment of the optimum length dipole to defeat a given enemy radar device has not been developed. The Navy recognized that an airborne chaff generator would have significant potential advantages over the present systems of deploying precut chaff. The main advantages would include l) the continuous or batch deployment of chaff; (2) on-site selection and control of both dipole length and thickness-width ratio distributions, thus allowing a chaff cloud custom tailored with respect to both radar cross section versus frequency and aerodynamic behavior; and (3) the capability for deployment of very long (up to perhaps 1 meter) dipoles.

Recently developed methods and apparatus for fabricating metal fibers directly from the molten state have the potential for development into an airborne chaff generating system. The methods of continuous casting metal fiber and filaments of interest here are known as melt spinning.

Many pieces of equipment have been developed for manufacturing metal fibers in a continuous manner. Great difficulty has been encountered in developing fibers from high melting point material. Several areas in the production of these fibers are critical such as the nozzle for spraying liquid metal, the chill block for receiving the liquid and the method for handling the continuous fibers. Multiple fiber apparatus for producing metal filaments have been developed such as US. Pat. No. 2,910,744 to R. B. Pond as the inventor. Several different aspects of his invention are shown and these deal primarily with a plurality of nozzles and a plurality of chill blocks for cooling areas.

As described in US. Pat. Nos. 2,910,744; 2,899,728 and 2,904,859, the chill block melt spinning method of continuous casting ribbon fibers consists of forming and directing a jet of molten material on to a rotating chill block where the jet is shaped and solidified as ribbon.

In seeking a more efficient, higher production rate melt spinning system than the prior art multiple orifice type, the flat-jet-nozzle composite chill block system was developed. Basically this system consists of a stable sheet forming device, such as a flat-jet-nozzle and a composite-type chill block. The function of the composite chill block is twofold; (l) to solidify the incoming uniform thickness liquid sheet and (2) to effect solid state slitting of the sheet to produce multiple ribbon fibers.

Solid state slitting is achieved by making different portions of the solidified sheet experience different dwell times. The dwell time is that period during which the formed ribbon resides (i.e., adheres) on the chill block surface. The dwell time is a function of fiber thickness, chill block surface finish, and the thermal properties of the chill block and solidified fiber. For a uniform thickness sheet of a given metal, the dwell time is controlled by the chill blocks surface finish andthermal properties (i.e., conductivity, specific heat, size and density). For a given surface velocity, dwell time and the point of release of the fiber from the chill block are directly related. Making the dwell time different for neighboring portions of a solidified sheet on the chill block surface introduces a shearing or tearing action in the sheet, thereby slitting it.

In order to select and control the melt spun fiber dimensions, it is advantageous to vary and control chill block surface velocity over the range of 20 to 400 feet per second. Acceptable chill-block diameters range from 4 to approximately 12 inches. Small diameter chill blocks do not provide sufficient circumference for fiber release and trajectory control. Only a limited portion of the large diameter chill blocks is utilized in casting the ribbon fibers; therefore, little is gained in increasing chill-block diameter beyond 12 inches.

In the chill block meltspinning system using one embodiment of the invention 4 or 8 inch-diameter chill blocks were mounted on a inch-diameter hollow shaft, which was driven by a variable speed h.p. motor. The range of chill block rotational speeds was from 60 to about 5000 rpm. This broad a range of rotational speeds is not required in a production unit, which will probably be either a fixed surface velocity system or one in which surface velocity is varied over one order of magnitude (i.e., from 200 to 2,000 rpm).

The finish on the chill block surface is an important factor. Release of the ribbon fiber becomes more difficult as the surface roughness increases. Thinner fibers are more difficult to discharge or release from the chill block and therefore, necessitate the use of smooth surface chill blocks. A practical and satisfactory surface finish is 2 to 5 microinches CLA.

In order to achieve steady-state operation, the chill block must be cooled; that is, the heat removed in solidifying the incoming jets must, in turn, be removed from the chill block. If chill block cooling is not provided, the chill block temperature increases until the jets no longer solidify on the chill block and molten droplets are formed. For aluminum, with a latent heat of fusion of calories/gram, auxiliary cooling of the chill block is demanded. One can anticipate a thermal energy of the order of to 200 calories per gram (55 to 90 Kcal/lb) of aluminum fiber produced. If the fiber production rate per orifice is 0.002 lb/second (0.9 gm/sec), the chill .block will receive energy at the rate of 100 to calories per second per orifice.

The function of the composite or stacked-type chill block is to solidify the incoming sheet jet and to effect solid-state slitting of the sheet, thereby producing multiple ribbon fibers. Solid-state slitting is achieved by making different portions of the solidified sheet experience different dwell times. The dwell time is that period during which the formed ribbon resides (i.e., adheres) on the chillblock surface. Typical dwell times associated with chill block melt spinning are of the order of 10 seconds.

The dwell time is a function of fiber thickness, chill block surface finish, and the thermal properties of the chill block and solidified fiber. For a uniform thickness sheet of a given metal, the dwell time is controlled by the chill blocks surface finish and thermal conductivity. For a given surface velocity, dwell time and the point of release of the fiber from the chill block are directly related, Making the dwell time different for neighboring portions of a solidified sheet on the chill block surface introduces a shearing or tearing action in the sheet, thereby slitting it.

The copper-steel and aluminum-steel composite chill blocks performed best and the better performance with these materials is probably a reflection that these chill block surfaces can be better prepared (i.e., more uniformly polished) than the other systems.

It is therefore an object of this invention to provide an improved chill block for producing a plurality of metal ribbon filaments in a continuous manner.

It is yet a further object of this invention to provide a rotating chill block having a surface of alternate bands of high and low heat conductivity portions for receiving a sheet of molten metal and to cool the molten sheet of metal while the sheet of metal is in contact with the high and low heat conductivity bands and thus provides a series of continuous fibers of metal by providing a shearing action between the portions of the sheet of different temperatures.

Still a further object of this invention is to provide an improved chill block for producing a plurality of metal fibers comprising, a central rotatable shaft having a major longitudinal axis, a body portion mounted on the shaft, a peripheral portion of the body portion having alternate bands of high and low heat conductivity positioned to receive a liquid metal sheet in contact with the alternate portions, means for cooling the peripheral portion so that the high conductivity portion when in contact with the liquid metal, cools the liquid metal to a solid state and the low conductivity portions cool the liquid metal at a slower rate so that shear flow is developed between solidifying portions of the metal sheet and a plurality of individual fibers are produced.

It is another object of this invention to provide an improved composite chill block for producing a plurality of metal fibers from a sheet of liquid metal comprising the improvement of providing a plurality of high and low heat conductivity bands on a rotatable member having high polished surface so that the time the liquid sheet is in contact with the polished surfaces provides different cooling rates to portions of the sheet and thus provides a shear action between the different portion of the sheet of liquid metal.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. 1, is a view of one chill block embodiment of the invention.

FIG. 2, is a side section view of the chill block along lines l] in FIG. 1.

The composite chill block generally designated as in FIGS. 1 and 2 is shown in position for receiving from a nozzle 11, a sheet 12 of molten metal. The block itself consists of a central shaft 13 rotatable about a longitudinal axis 14. First and second end plates 15 and 16 are mounted on shaft 13. An outer composite housing 17 is affixed between end members 15 and 16 and held in place after assembly by a series of bolts 19. Portion 17 is composed of alternate bands or rings of high and low heat conductivity material. The outer two large bands 15, 16 are of low heat conductivity material and bands 22 are of high heat conductivity material. The bands 23 innerspaced between bands 22 are a series of bands of low heat conductivity. Shaft 13 is provided with port 25 thru which cooling liquid such as water may be piped into a central portion of the chill block 10. The cooling material would be piped into a shaft 13 by connections not shown for the sake of clarity. Similarly, the cooling liquid is not shown in the inside of the chill block so that the structure thereto might be more clearly shown. Means for circulating the cooling liquid and allowing it to exit from the chill block could also be provided but is not shown for the sake of clarity.

As set forth above the peripheral portion of the stacked chill block 15 designated as 22 and 23 has a highly polished surface. The more polished the surface the better the shear between the alternate bands of high and low heat conductivity metal. The rotation of the shaft 13 can be controlled as can the flow of the metal sheet to produce individual fibers up to one meter. Thus a portable chaff generator utilizing the improved chill block can be airborne and can on-site generate the proper radar chaff for countermeasures.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

1. An improved chill block for producing a plurality of metal ribbon fibers comprising:

a. a central rotatable shaft having a major longitudinal axis;

b. a generally cylindrical body portion having a peripheral surface portion and end portions mounted on said shaft;

c. said peripheral surface portion constructed of alternate bands of high and low heat conductivity material of the same external diameter to form a smooth continuous unbroken surface from either end of said cylindrical body portion;

(1. means for depositing a liquid metal sheet on said peripheral surface portion; and

e. cooling means to cool said peripheral portion so that said high conductivity portion when in contact with said liquid metal sheet rapidly cools said liquid metal sheet to a solid state and said low conductivity portions contacting said liquid metal sheet slowly cools said liquid metal sheet so that shear flow is developed between solidifying portions of said liquid metal sheet for producing a plurality of metal ribbon fibers.

2. The improved chill block of claim 1 wherein said central shaft and body portions of said chill block are hollow to provide for the flow of a liquid coolant to maintain the high conductivity portions of said peripheral portions at a temperature sufficient to cool the liquid metal.

3. The improved chill block of claim 2 wherein there is provided means for rotating said shaft at a speed so that the dwell time of the liquid metal on the high conductivity portions is sufficient to cool the liquid sheet to a group of individual solid fibers.

4. The improved chill block of claim 3 wherein said peripheral portion of said body portion is polished to a surface finish between two and five microinches CLA.

5. The improved chill block of claim 4 wherein the velocity of said peripheral portion is between 20 feet per second and 400 feet per second.

6. The improved chill block of claim 5 wherein the diameter of said chill block is between 4 inches and 12 inches. 

1. An improved chill block for producing a plurality of metal ribbon fibers comprising: a. a central rotatable shaft having a major longitudinal axis; b. a generally cylindrical body portion having a peripheral surface portion and end portions mounted on said shaft; c. said peripheral surface portion constructed of alternate bands of high and low heat conductivity material of the same external diameter to form a smooth continuous unbroken surface from either end of said cylindrical body portion; d. means for depositing a liquid metal sheet on said peripheral surface portion; and e. cooling means to cool said peripheral portion so that said high conductivity portion when in contact with said liquid metal sheet rapidly cools said liquid metal sheet to a solid state and said low conductivity portions contacting said liquid metal sheet slowly cools said liquid metal sheet so that shear flow is developed between solidifying portions of said liquid metal sheet for producing a plurality of metal ribbon fibers.
 2. The improved chill block of claim 1 wherein said central shaft and body portions of said chill block are hollow to provide for the flow of a liquid coolant to maintain the high conductivity portions of said peripheral portions at a temperature sufficient to cool the liquid metal.
 3. The improved chill block of claim 2 wherein there is provided means for rotating said shaft at a speed so that the dwell time of the liquid metal on the high conductivity portions is sufficient to cool the liquid sheet to a group of individual solid fibers.
 4. The improved chill block of claim 3 wherein said peripheral portion of said body portion is polished to a surface finish between two and five microinches CLA.
 5. The improved chill block of claim 4 wherein the velocity of said peripheral portion is between 20 feet per second and 400 feet per second.
 6. The improved chill block of claim 5 wherein the diameter of said chill block is between 4 inches and 12 inches. 